The present invention generally relates to a resist composition that can be developed by a basic developing liquid and a fabrication process of a semiconductor device using such a resist composition.
With the advancement in the art of device miniaturization, recent semiconductor integrated circuits designated as LSIs or VLSIs are now patterned with sub-micron line widths. Further, intensive investigations are being made on so-called sub-halfmicron devices that use a minimum pattern width of smaller than 0.5 μm.
In order to fabricate such sub-halfmicron devices, it is essential to reduce the wavelength of the optical radiation that is used for exposing a pattern on a semiconductor substrate, from a conventional, normal ultraviolet wavelength to a far-ultraviolet wavelength. Further, investigations are being made also on the exposure process that uses a deep ultraviolet wavelength radiation. Associated with such a shift in the wavelength of the optical radiation used for photolithography, there is an urgent demand for a resist composition that shows a reduced optical absorption in such a very short wavelength band and simultaneously a high dry etching resistance and a high sensitivity.
In recent years, intensive studies have been made on the photolithography that uses a novel optical source of KrF excimer laser. A KrF excimer laser produces an optical radiation with a wavelength of 248 nm, and the technology of the KrF excimer laser photolithography is now being reduced to practice. In relation to the development of photolithography that uses such a very short wavelength optical radiation, there is proposed a concept of chemical amplification resist (J. M. J. Frechet, et al., Proc. Microcircuit Eng., 260 (1982), H. Ito, et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86 (1983), H. Ito, et a., “Polymer in Electronics,” ACS Symposium Series 242, T. Davidson ed., ACS, 11 (1984), U.S. Pat. No. 4,491,628) that shows a high sensitivity and high resolution in the exposure process conducted by such very short wavelength optical radiations.
The basic concept of chemical amplification resist is to increase the apparent quantum yield by inducing a catalytic reaction in the resist film.
In the example of widely studied, as well as widely used, chemical amplification positive type resist, in which a PAG (photo acid generator) is added to t-butoxycarbonyl (t-BOC) polyvinyl phenol (PVP), the t-BOC group functions as a protective group and causes a desorption as a result of the post exposure baking (PEB) process conducted after the exposure. As a result of the PEB process, isobutene and carbon dioxide are formed. As such a desorption process releases a protonic acid, a chain reaction is triggered in the resist composition with regard to the deblocking reaction, and the polarity of the resist is changed significantly in the exposed part of the resist film. Thus, by applying a suitable developing liquid to the resist film thus exposed, a resist pattern is successfully formed.
On the other hand, recent attempts of forming semiconductor devices of still higher integration density such as Gbit DRAMs, have urged an investigation on the photolithography that uses a still shorter wavelength optical radiation of 193 nm wavelength band produced by an ArF excimer laser. In the photolithographic process that uses such a very short wavelength optical radiation, the problem of strong optical absorption by the resist is inevitable as long as a phenolic polymer resin is used for the resist base. Thus, there is an urgent demand for a resist that is applicable to such a very short-wavelength optical radiation.
While there are various chemical amplification resists studied for application to an exposure process conducted with the optical radiation of 193 nm wavelength, most of the conventionally studied resists are based on a methacrylic resin that has an ester group called polycyclic alicyclic group. Examples thereof are adamantane, isobornane, tricyclodecane, and others. See for example, Nozaki, K., et al, Chem. Mater., 1994, 6, 1492-1498, Nakano, K., et al, Proc. SPIE, 1994, 2195, 194-204, and Allen, R. D., et al, Proc. SPIE, 1994, 2438, 474-485. The foregoing conventional resists successfully realize the necessary dry-etching resistance that is essential for a resist, by incorporating alicyclic ester group into the base resin.
On the other hand, the foregoing conventional resists have suffered from the problems, associated with the use of the alicyclic group in the resin,such as a peeling-off of the resist during the developing process or an insufficient dissolving of the exposed area to an alkaline developer. In order to overcome the foregoing problems, there are proposals such as incorporation of carboxylic acid unit into the base resin or using a diluted developing liquid. Further, there are proposals for mixing an alcohol such as isopropyl alcohol to the developer.
Further, there is a report of a chemical amplification resist composition that solves the foregoing problems successfully (Nozaki, K., et al., Jpn. J. Appl. Phys., 35, 1996, L528-L530). The reported resist uses mevalonic lactone and 2-methyl-2-adamantanol for the protective group of the carboxylic acid in the base resin.
In the foregoing resist composition, both of the protective groups cause deprotection, while such deprotection enables a development of the resist by using a standard alkaline developer. As mevalonic lactone has a strong polarity, the resist composition shows an improved adhesion to a substrate. Further, the resist composition has a sufficient sensitivity and enables formation of ultra-fine patterns without swelling.
On the other hand, there has been a problem in the foregoing conventional resist composition in that the synthesis of mevalonic lactone methacrylate has to be conducted at a low temperature, and that the mevalonic lactone source material is expensive.